Navigating a surgical instrument

ABSTRACT

An instrument tracking device for cooperating with an instrument during a surgical procedure where the instrument has an elongated body extending along a first longitudinal axis and including a working member at a distal tip includes a body having a distal end and a proximal end. An opening can be formed through the body along a second longitudinal axis. The opening can define a passthrough in the body from the distal end to the proximal end. A first tracking coil can be disposed in the body and can define a first tracking coil axis that is substantially coaxial with the second longitudinal axis of the body. A connection mechanism cooperates between the elongated housing and the body that secures the body to the elongated housing of the instrument upon passing at least a portion of the elongated housing through the passthrough of the body in an assembled position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/400,951 filed on Mar. 10, 2009. The disclosure of the aboveapplication is incorporated herein by reference.

FIELD

The present disclosure relates generally to image-guided surgerysystems, and particularly to a removable electromagnetic instrumenttracking device that selectively couples with a surgical handpiece.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Surgical procedures can be performed on anatomies such as the humananatomy for providing a therapy to the anatomy. One area of surgeryincludes procedures performed on facial cavities of a patient such as onthe ear, nose or throat (ENT). In such a procedure, a working membersuch as a shaver, bur, or other tool connected to an instrument (e.g., ahandpiece) may be inserted into such a cavity to perform a shapingprocedure for example. As it is desirable to minimize trauma produced bysuch procedures, it is favorable to avoid any supplemental incisions orother axis portals to be formed in the patient tissue.

Because the viewing angle of a surgeon at the area of interest can beobscured by the surrounding tissue of the cavity, the ability of asurgeon to effectively apply a therapy can be reduced. Therefore, it isdesirable to provide a mechanism so that a surgeon can provide a therapywithout minimization or reduction of effectiveness of the procedure orin viewing the area to apply the therapy. Navigation of instrumentsrelative to the anatomy can be used.

In some navigation systems, instruments are provided with trackingdevices. Sometimes however such tracking devices can be difficult tomanipulate or cumbersome to the instrument. In other instances, thetracking devices can protrude a significant distance from the instrumentand interfere with a surgeon's sight line. Other tracking devices failto provide accurate positional information in 3-dimensional space or maybe susceptible to electromagnetic interference because of metal objects.

SUMMARY

An instrument tracking device for cooperating with an instrument duringa surgical procedure where the instrument has an elongated bodyextending along a first longitudinal axis and including a working memberat a distal tip includes a body having a distal end and a proximal end.An opening can be formed through the body along a second longitudinalaxis. The opening can define a passthrough in the body from the distalend to the proximal end. A first tracking coil can be disposed in thebody and can define a first tracking coil axis that is substantiallycoaxial with the second longitudinal axis of the body. The firsttracking coil can generate an output signal indicative of a position ofthe working member. A connection mechanism cooperates between theelongated housing and the body that secures the body to the elongatedhousing of the instrument upon passing at least a portion of theelongated housing through the passthrough of the body in an assembledposition.

According to additional features, the first tracking coil can define afirst tracking coil plane. A second tracking coil can be disposed in thebody. The second tracking coil can define a second tracking coil planethat is substantially orthogonal relative to the first tracking coilplane. The second and third coils can be disposed in the body at aradially offset position relative to the first tracking coil. The firstand second longitudinal axes can be collinear in the assembled position.

According to other features, a third tracking coil can be disposed inthe body. The third tracking coil can define a third tracking coil planethat is substantially orthogonal to the first and second tracking coilplanes. The second tracking coil can define a second tracking coil axis.The third tracking coil can define a third tracking coil axis. Thesecond and third tracking coil axes can be substantially perpendicular.

In one configuration, the body can include a conical section thatextends radially outwardly from the distal end to the proximal end. Thesecond and third tracking coils can be offset toward the proximal end ofthe body relative to the first tracking coil. The body can include apair of lobes that project radially from the proximal end of the bodyand alternately accommodate the second and third coils, respectively.The body can include an extension portion formed intermediate of thepair of lobes that accommodates a wire harness. According to oneconfiguration, the body can comprise a base having the first, second andthird tracking coils disposed therein and a cap that covers the base.The base and the cover can be formed of plastic.

According to one configuration, the body can be low profile relative tothe instrument, such that an outermost distance of the body measuredradially from the first tracking coil axis is less than three times aninner diameter of the opening. The instrument can comprise a surgicalhandpiece. The working member can comprise a blade or a bur. In oneconfiguration, the body can be removably attached to the longitudinalbody of the instrument with an adhesive. In one example, the workingmember can be removable from the body. In another example, the workingmember can be fixed and non-removable relative to the body.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is an environmental view of a surgical navigation system,according to various embodiments;

FIG. 2A is a perspective view of an exemplary handpiece having aworkpiece such as a blade and shown with an electromagnetic trackingdevice in an assembled position on a distal end of the handpiece;

FIG. 2B is a perspective view of a blade assembly including the bladeshown in FIG. 2A;

FIG. 3A is an exploded view of the instrument tracking deviceillustrating a body having a base and a cap;

FIG. 3B is a perspective view of an instrument tracking device having abody according to additional features;

FIG. 4 is a longitudinal end view of the electromagnetic tracking deviceillustrated in FIG. 3A and shown with the cap in phantom;

FIG. 5 is a sectional view of the instrument tracking device taken alongline 5-5 of FIG. 4;

FIG. 6 is a sectional view of the electromagnetic instrument trackingdevice taken along line 6-6 of FIG. 4;

FIG. 7 is a perspective view of the electromagnetic instrument trackingdevice shown operatively connected with a wire harness and electricalconnector and shown removed from a bag; and

FIG. 8 is a longitudinal end view of an electromagnetic tracking deviceaccording to additional features.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses.Initially, one skilled in the art will understand that the system andapparatus disclosed herein can be used in any appropriate procedure.Although a head frame is illustrated attached to a cranium and imagedata is illustrated for a cranium, any appropriate portion of theanatomy can be imaged. Moreover, a head frame may not be necessary and adynamic reference frame can be attached to any appropriate structure,such as a bone screw, an adhesive base, an orifice, etc. Furthermore,the following discussion is directed toward instrumentation used duringa surgical procedure focused on a sinus cavity of a patient. It will beappreciated however that the teachings may be similarly applied to otherear, nose, throat (ENT) procedures or other surgical procedures ingeneral, such as, but not limited to anterior skull base surgery.

With initial reference to FIG. 1, an electromagnetic (EM) image-guidedsurgery system according to one example of the present teachings isshown and generally identified at reference numeral 10. The EMimage-guided surgery system 10 can generally include an instrument suchas a handpiece 12 having a removable EM instrument tracking device 14configured to communicate with an exemplary navigation system 20. Thenavigation system 20 can be used to track the location of the handpiece12 relative to a patient 22 to assist in a surgical procedure. As willbe described in greater detail herein, the EM instrument tracking device14 can receive a signal, transmit a signal, or combinations thereof toprovide information to the navigation system 20 to determine a locationof the EM instrument tracking device 14. Prior to discussing in detailthe EM instrument tracking device 14 according to the present teachings,a general discussion of the exemplary navigation system 20 is warranted.

The navigation system 20 can include an imaging device 24 that is usedto acquire pre-, intra-, or post-operative or real-time image data ofthe patient 22. The image data acquired with the imaging device 24 canbe used as part of the image data in the EM image-guided surgery system10. In addition, data from atlas models can be used to produce patientimages, such as those disclosed in U.S. patent application Ser. No.10/687,539, filed Oct. 16, 2003, now U.S. Pat. App. Pub. No.2005/0085714, entitled “METHOD AND APPARATUS FOR SURGICAL NAVIGATION OFA MULTIPLE PIECE CONSTRUCT FOR IMPLANTATION”, incorporated herein byreference. The imaging device 24 is, for example, a fluoroscopic X-rayimaging device that may be configured as a C-arm 26 having an X-raysource 28, an X-ray receiving section 30, an optional calibration andtracking target 32 and optional radiation sensors. The calibration andtracking target 32 includes calibration markers (not illustrated). Imagedata may also be acquired using other imaging devices, such as thosediscussed herein.

In the exemplary configuration, the EM instrument tracking device 14 iscoupled to the handpiece 12 such that the navigation system 20 can trackthe location of the handpiece 12, relative to a patient 22 to assist ina surgical procedure. As will be described, the EM instrument trackingdevice 14 can be either removably attached or fixed (non-removablyattached) to the handpiece 12. It should be further noted that the EMinstrument tracking device 14 can be coupled to other devices including:catheters, probes, needles, leads, implants, etc., for tracking theirlocation with the navigation system 20. Moreover, the navigated devicemay be used in any region of the body. The navigation system 20 and thevarious devices may be used in any appropriate procedure, such as onethat is generally minimally invasive, arthroscopic, percutaneous,stereotactic, or an open procedure. Although an exemplary navigationsystem 20 including the imaging system 24 are discussed herein, oneskilled in the art will understand that the disclosure is merely forclarity of the present discussion and any appropriate imaging system,navigation system, patient specific data, and non-patient specific datacan be used. For example, the intraoperative imaging system can includean MRI imaging system, such as the PoleStar® MRI or an O-arm™ imagingsystem both sold by Medtronic, Inc. It will be understood that thenavigation system 20 can incorporate or be used with any appropriatepreoperatively or intraoperatively acquired image data.

An optional imaging device controller 34 may control the imaging device24, such as the C-arm 26, which can capture the x-ray images received atthe X-ray receiving section 30 and store the images for later use. Thecontroller 34 may also be separate from the C-arm 26 and can be part ofor incorporated into a work station 36. The controller 34 can controlthe rotation of the C-arm 26. For example, the C-arm 26 can move in thedirection of arrow 38 or rotate about a longitudinal axis 22 a of thepatient 22, allowing anterior or lateral views of the patient 22 to beimaged. Each of these movements involves rotation about a mechanicalaxis 39 of the C-arm 26. The movements of the imaging device 24, such asthe C-arm 26 can be tracked with a tracking device 40.

In the example of FIG. 1, the longitudinal axis 22 a of the patient 22is substantially in line with the mechanical axis 39 of the C-arm 26.This enables the C-arm 26 to be rotated relative to the patient 22,allowing images of the patient 22 to be taken from multiple directionsor in multiple planes. An example of a fluoroscopic C-arm X-ray devicethat may be used as the imaging device 24 is the “Series 9600 MobileDigital Imaging System,” from GE Healthcare, (formerly OEC MedicalSystems, Inc.) of Salt Lake City, Utah. Other exemplary fluoroscopesinclude bi-plane fluoroscopic systems, ceiling mounted fluoroscopicsystems, cath-lab fluoroscopic systems, fixed C-arm fluoroscopicsystems, isocentric C-arm fluoroscopic systems, 3D fluoroscopic systems,intraoperative O-arm™ imaging systems, etc.

The C-arm X-ray imaging system 26 can be any appropriate system, such asa digital or CCD camera, which are well understood in the art. Twodimensional fluoroscopic images that may be taken by the imaging device24 are captured and stored in the imaging device 24. Multipletwo-dimensional images taken by the imaging device 24 may also becaptured and assembled to provide a larger view or image of a wholeregion of the patient 22, as opposed to being directed to only a portionof a region of the patient. The multiple image data can include multiple2D slices that are assembled into a 3D model or image.

The image data can then be forwarded from the imaging device 34 to thenavigation computer and/or processor controller or work station 36having a display device 42 to display image data 44 and a user interface46. The work station 36 can also include or be connected to an imageprocessor, navigation processor, and a memory to hold instruction anddata. The work station 36 can include an optimization processor thatassists in a navigated procedure. It will also be understood that theimage data is not necessarily first retained in the controller 34, butmay also be directly transmitted to the work station 36. Moreover,processing for the navigation system 20 and optimization can all be donewith a single or multiple processors all of which may or may not beincluded in the work station 36.

The work station 36 provides facilities for displaying the image data 44as an image on the display device 42, saving, digitally manipulating, orprinting a hard copy image of the received image data. The userinterface 46, which may be a keyboard, mouse, touch pen, touch screen orother suitable device, allows a physician or user 50 to provide inputsto control the imaging device 24, via the controller 34, or adjust thedisplay settings of the display 42. The work station 36 may also directthe controller 34 to adjust the rotational axis 38 of the C-arm 26 toobtain various two-dimensional images in different planes in order togenerate representative two-dimensional and three-dimensional images.

While the imaging device 24 is shown in FIG. 1, any other alternative2D, 3D or 4D imaging modality may also be used. For example, any 2D, 3Dor 4D imaging device, such as isocentric fluoroscopy, bi-planefluoroscopy, ultrasound, computed tomography (CT), multi-slice computedtomography (MSCT), magnetic resonance imaging (MRI), positron emissiontomography (PET), optical coherence tomography (OCT) (a more detaileddiscussion on optical coherence tomography (OCT), is set forth in U.S.Pat. No. 5,740,808, issued Apr. 21, 1998, entitled “Systems And MethodsFor Guiding Diagnostic Or Therapeutic Devices In Interior TissueRegions” which is hereby incorporated by reference), intra-vascularultrasound (IVUS), intra-operative CT, single photo emission computedtomography (SPECT), planar gamma scintigraphy (PGS). Additional imagingsystems include intraoperative MRI systems such as the PoleStar® MRIsystem sold by Medtronic, Inc. Further systems include the O-Arm™imaging system sold by Medtronic, Inc. The images may also be obtainedand displayed in two, three or four dimensions. In more advanced forms,four-dimensional surface rendering regions of the body may also beachieved by incorporating patient data or other data from an atlas oranatomical model map or from pre-operative image data captured by MRI,CT, or echocardiography modalities.

Image datasets from hybrid modalities, such as positron emissiontomography (PET) combined with CT, or single photon emission computertomography (SPECT) combined with CT, could also provide functional imagedata superimposed onto anatomical data to be used to confidently reachtarget sights within the patient 22. It should further be noted that theimaging device 24, as shown in FIG. 1, provides a virtual bi-plane imageusing a single-head C-arm fluoroscope as the imaging device 24 by simplyrotating the C-arm 26 about at least two planes, which could beorthogonal planes to generate two-dimensional images that can beconverted to three-dimensional volumetric images. By acquiring images inmore than one plane, an icon representing the location of an impacter,stylet, reamer driver, taps, drill, or other instrument, or probeintroduced and advanced in the patient 22, may be superimposed in morethan one view on display 42 allowing simulated bi-plane or evenmulti-plane views, including two and three-dimensional views.

Four-dimensional (4D) image information can be used with the navigationsystem 20 as well. For example, the user 50 can use a physiologicsignal, which can include Heart Rate (EKG), Breath Rate (Breath Gating)and combine this data with image data 44 acquired during the phases ofthe physiologic signal to represent the anatomy at various stages of thephysiologic cycle. For example, the brain pulses (and therefore moves)with each heartbeat. Images can be acquired to create a 4D map of thebrain, onto which atlas data and representations of the instrument canbe projected. This 4D data set can be matched and co-registered with thephysiologic signal (EKG) to represent a compensated image within the EMimage-guided surgery system 10. The image data registered with the 4Dinformation can show the brain (or anatomy of interest) moving duringthe cardiac or breath cycle. This movement can be displayed on thedisplay 42 as the image data 44.

Likewise, other imaging modalities can be used to gather the 4D datasetto which pre-operative 2D and 3D data can be matched. One need notnecessarily acquire multiple 2D or 3D images during the physiologiccycle of interest (breath or heart beat). Ultrasound imaging or other 4Dimaging modalities can be used to create an image data that allows for asingular static pre-operative image to be matched via image-fusiontechniques and/or matching algorithms that are non-linear to match thedistortion of anatomy based on the movements during the physiologiccycle. The combination of a dynamic reference frame 60 and 4Dregistration techniques can help compensate for anatomic distortionsduring movements of the anatomy associated with normal physiologicprocesses.

The EM image-guided surgery system 10 includes a localizer, such as acoil array 64 and/or second tracking coil array 66, a coil arraycontroller 68, a navigation handpiece interface 70, the handpiece 12(e.g. catheter, needle, or instruments, as discussed herein) and thedynamic reference frame 60. The dynamic reference frame 60 can include adynamic reference frame holder or EM, ENT head frame 74 and a removableEM, ENT patient tracker 76. In one example, the EM, ENT patient tracker76 can be used with Synergy™ ENT software provided by Medtronic, Inc.,on a computer-assisted surgery system (such as the EM image-guidedsurgery system 10 disclosed herein) to track the position of a patient'shead during surgery. The EM, ENT head frame 74 can be mounted to thepatient's forehead, such as by using an adhesive pad, a silicone pad anda frame strap. Alternatively, the head frame 74 can include a trackingdevice that can be formed integrally with the head frame 74.

Moreover, the DRF 60 can be provided as separate pieces and can bepositioned at any appropriate position on the anatomy. For example, theENT patient tracker 76 of the DRF can be fixed to the skin of thepatient 22 with an adhesive. Also, the DRF 60 can be positioned near aleg, arm, etc. of the patient 22. Thus, the DRF 60 does not need to beprovided with a head frame or require any specific base or holdingportion.

The tracking devices 14, 40, 76 or any tracking device as discussedherein, can include a sensor, a transmitter, or combinations thereof.Further, the tracking devices can be wired or wireless to provide asignal emitter or receiver within the navigation system 20. For example,any or all of the tracking devices 14, 40, 76 can include anelectromagnetic coil to sense a field produced by the localizing array64, 66. Nevertheless, one will understand that the tracking device (14,40, 76) can receive a signal, transmit a signal, or combinations thereofto provide information to the navigation system 20 to determine alocation of the tracking device 14, 40, 76. Therefore, as used herein,“generating an output signal” is used to mean any combination ofreceiving a signal, transmitting a signal or combinations thereof. Thenavigation system 20 can then determine a position of the handpiece 12or tracking device 14, 40, 76 to allow for navigation relative to thepatient 22 and patient space. One suitable navigation system isdisclosed in commonly owned U.S. Publication No 2008/0132909, filed Jun.5, 2008, the contents of which are expressly incorporated herein byreference. One suitable commercially available navigation systemincludes “STEALTHSTATION® AXIEM™ Navigation System.

The coil arrays 64, 66 may also be supplemented or replaced with amobile localizer. The mobile localizer may be one such as that describedin U.S. patent application Ser. No. 10/941,782, filed Sep. 15, 2004, nowU.S. Pat. App. Pub. No. 2005/0085720, entitled “METHOD AND APPARATUS FORSURGICAL NAVIGATION”, herein incorporated by reference. As is understoodthe localizer array can transmit signals that are received by thetracking devices 14, 40, 76. The tracking device 14, 40, 76 can thentransmit or receive signals based upon the transmitted or receivedsignals from or to the array 64, 66.

Further included in the navigation system 20 may be an isolator circuitor assembly (not illustrated separately). The isolator circuit orassembly may be included in a transmission line to interrupt a linecarrying a signal or a voltage to the navigation handpiece interface 70.Alternatively, the isolator circuit included in the isolator box may beincluded in the navigation handpiece interface 70, the handpiece 12, thedynamic reference frame 60, the transmission lines coupling the devices,or any other appropriate location. The isolator assembly is operable toisolate any of the instruments or patient coincidence instruments orportions that are in contact with the patient 22 should an undesirableelectrical surge or voltage take place.

The EM image-guided surgery system 10 uses the coil arrays 64, 66 tocreate an electromagnetic field used for navigation. The coil arrays 64,66 can include a plurality of coils that are each operable to generatedistinct electromagnetic fields into the navigation region of thepatient 22, which is sometimes referred to as patient space.Representative electromagnetic systems are set forth in U.S. Pat. No.5,913,820, entitled “Position Location System,” issued Jun. 22, 1999 andU.S. Pat. No. 5,592,939, entitled “Method and System for Navigating aCatheter Probe,” issued Jan. 14, 1997, each of which are herebyincorporated by reference.

The coil array 64 is controlled or driven by the coil array controller68. The coil array controller 68 drives each coil in the coil array 64in a time division multiplex or a frequency division multiplex manner.In this regard, each coil may be driven separately at a distinct time orall of the coils may be driven simultaneously with each being driven bya different frequency.

Upon driving the coils in the coil array 64 with the coil arraycontroller 68, electromagnetic fields are generated within the patient22 in the area where the medical procedure is being performed, which isagain sometimes referred to as patient space. The electromagnetic fieldsgenerated in the patient space induce currents in the EM instrumenttracking device 14 and patient tracking device 76. These induced signalsfrom the tracking devices 14, 40, 76 are delivered to the navigationhandpiece interface 70 and subsequently forwarded to the coil arraycontroller 68. The navigation handpiece interface 70 can also includeamplifiers, filters and buffers to directly interface with the EMinstrument tracking device 14 on the handpiece 12. Alternatively, the EMinstrument tracking device 14, or any other appropriate portion, mayemploy a wireless communications channel, such as that disclosed in U.S.Pat. No. 6,474,341, entitled “Surgical Communication Power System,”issued Nov. 5, 2002, herein incorporated by reference, as opposed tobeing coupled directly to the navigation handpiece interface 70.

Various portions of the navigation system 20, such as the handpiece 12,or the dynamic reference frame 60, are equipped with at least one, andgenerally multiple, EM or other tracking devices (i.e., such as 14 and40), that may also be referred to as localization sensors. The EMtracking devices 14, 40 can include one or more coils that are operablewith the EM localizer arrays 64, 66. For example, the EM instrumenttracking device 14 includes three coils as will be described. Anadditional representative alternative localization and tracking systemis set forth in U.S. Pat. No. 5,983,126, entitled “Catheter LocationSystem and Method,” issued Nov. 9, 1999, which is hereby incorporated byreference. Alternatively, the localization system may be a hybrid systemthat includes components from various systems.

The dynamic reference frame 60 may be fixed to the patient 22 adjacentto the region being navigated so that any movement of the patient 22 isdetected as relative motion between the coil array 64, 66 and thedynamic reference frame 60. The dynamic reference frame 60 can beinterconnected with the patient 22 in any appropriate manner, includingthose discussed herein. Relative motion is forwarded to the coil arraycontroller 68, which updates registration correlation and maintainsaccurate navigation, further discussed herein. The dynamic referenceframe 60 may include any appropriate tracking sensor. Therefore, thedynamic reference frame 60 may also be optical, acoustic, etc. If thedynamic reference frame 60 is electromagnetic it can be configured as apair of orthogonally oriented coils, each having the same center or maybe configured in any other non-coaxial or co-axial coil configurations.

Prior to tracking the EM instrument tracking device 14, patientregistration is performed. Patient registration is the process ofdetermining how to correlate the position of the handpiece 12 relativeto the patient 22 to the position on the diagnostic or image data. Toregister the patient 22, the physician or user 50 may use pointregistration by selecting and storing particular points (e.g. fiducialpoints) from the image data and then touching the corresponding pointson the patient's anatomy (i.e., in this example various facial featuressuch as the nose, lips, chin, cheeks or other locations near the nose)with the handpiece 12. The navigation system 20 analyzes therelationship between the two sets of points that are selected andcomputes a match, which correlates every point in the image data withits corresponding point on the patient's anatomy or the patient space.

The points that are selected to perform registration are the fiducialmarkers or landmarks, such as anatomical landmarks. Again, the landmarksor fiducial points are identifiable on the images and identifiable andaccessible on the patient 22. The landmarks can be artificial landmarksthat are positioned on the patient 22. The artificial landmarks, such asthe fiducial markers, can also form part of the dynamic reference frame60, such as those disclosed in U.S. Pat. No. 6,381,485, entitled“Registration of Human Anatomy Integrated for ElectromagneticLocalization,” issued Apr. 30, 2002, herein incorporated by reference.

The patient 22 can include one or a plurality of fiducial markers (notspecifically shown) affixed to the anatomy of a patient 22, such as acranium. It will be understood that any appropriate number of thefiducial markers can be affixed to the patient 22 and in any appropriatelocation. The fiducial markers can be randomly attached to the patient22 or attached in specific locations.

The fiducial markers can include any appropriate marker to beinterconnected with the patient 22. For example, the makers sold by IZIMedical Products, Baltimore, Md. can be used. The markers can include anadhesive base that is adhered to the cranium. The fiducial markers canbe associated or connected to the patient 22 with an adhesive, mountingscrew, clamp, etc. According to various embodiments, the fiducialmarkers can be attached to the patient 22 prior to acquiring image datawith an adhesive in a selected manner. The fiducial markers can beplaced in predetermined locations or in random locations for imaging.The fiducial marker can also include a fiducial divot or identificationdivot. Once registration is performed, the navigation system 20 is readyto track the EM instrument tracking device 14.

Briefly, the navigation system 20 operates as follows. The navigationsystem 20 creates a translation map between all points in the image datagenerated from the imaging device 24 which can include external andinternal portions, and the corresponding points in the patient's anatomyin patient space. After this map is established, whenever the trackedhandpiece 12 is used, the work station 36 in combination with the coilarray controller 68 uses the translation map to identify thecorresponding point on the image data or atlas model, which is displayedon display 42. This identification is known as navigation orlocalization. An icon representing the localized point or instruments isshown on the display 42 within several two-dimensional image planes, aswell as on three and four dimensional images and models.

To enable navigation, the navigation system 20 must be able to detectboth the position of the patient's anatomy and the position of thehandpiece 12 (or EM instrument tracking device 14) attached to thehandpiece 12. Knowing the location of these two items allows thenavigation system 20 to compute and display the position of thehandpiece 12 or any portion thereof (i.e., a shaver blade as will bedescribed) in relation to the patient 22. The EM image-guided surgerysystem 10 is employed to track the handpiece 12 and the anatomysimultaneously.

The EM image-guided surgery system 10 essentially works by positioningthe coil array 64, 66 adjacent to the patient 22 to generate a magneticfield, which can be low energy, and generally referred to as anavigation field. Because every point in the navigation field or patientspace is associated with a unique field strength, the EM image-guidedsurgery system 10 can determine the position of the handpiece 12 bymeasuring the field strength at the location of the EM instrumenttracking device 14. The dynamic reference frame 60 is fixed to thepatient 22 to identify the location of the patient 22 in the navigationfield. The EM image-guided surgery system 10 continuously recomputes orrecalculates the relative position of the dynamic reference frame 60 andthe handpiece 12 during localization and relates this spatialinformation to patient registration data to enable navigation of thehandpiece 12 within and/or relative to the patient 22. Navigation caninclude image guidance or imageless guidance.

The navigation system 20 may also perform registration using anatomicsurface information or path information as is known in the art (and maybe referred to as auto-registration). The EM image-guided surgery system10 may also perform 2D to 3D registration by utilizing the acquired 2Dimages to register 3D volume images by use of contour algorithms, pointalgorithms or density comparison algorithms, as is known in the art. Anexemplary 2D to 3D registration procedure is set forth in U.S. Ser. No.10/644,680, now U.S. Pat. App. Pub. No. 2004/0215071, entitled “Methodand Apparatus for Performing 2D to 3D Registration” filed on Aug. 20,2003, hereby incorporated by reference.

In order to maintain registration accuracy, the navigation system 20continuously tracks the position of the patient 22 during registrationand navigation. This is because the patient 22, dynamic reference frame60, and transmitter coil array 64, 66 may all move during the procedure,even when this movement is not desired. Alternatively the patient 22 maybe held immobile once the registration has occurred, such as with afixed head frame. Therefore, if the navigation system 20 did not trackthe position of the patient 22 or area of the anatomy, any patientmovement after registration would result in inaccurate navigation withinthat image. The dynamic reference frame 60 allows the EM image-guidedsurgery system 10 to register and track the anatomy. Because the dynamicreference frame 60 is rigidly fixed to the patient 22, any movement ofthe anatomy or the coil array 64, 66 is detected as the relative motionbetween the coil array 64, 66 and the dynamic reference frame 60. Thisrelative motion is communicated to the coil array controller 68, via thenavigation handpiece interface 70, which updates the registrationcorrelation to thereby maintain accurate navigation.

The navigation system 20 can be used according to any appropriate methodor system. For example, image data, atlas or 3D models may be registeredrelative to the patient and patient space, as discussed further herein.Generally, the navigation system 20 allows the images on the display 42to be registered and accurately display the real time location of thevarious instruments and other appropriate items. In addition, thehandpiece 12 may be used to register the patient space to thepre-acquired image data or the atlas or 3D models. In addition, thedynamic reference frame 60 may be used to ensure that any planned orunplanned movement of the patient or the array 64, 66 is determined andused to correct the image on the display 42.

To obtain a maximum reference, it can be selected to fix the dynamicreference frame 60 in each of at least 6 degrees of freedom. Thus, thedynamic reference frame 60 can be fixed relative to axial motion X,translational motion Y, rotational motion Z, yaw, pitch, and rollrelative to the portion of the patient 22 to which it is attached. Anyappropriate coordinate system can be used to describe the variousdegrees of freedom. Fixing the dynamic reference frame relative to thepatient 22 in this manner can assist in maintaining maximum accuracy ofthe navigation system 20.

As mentioned briefly above, the display 42 can display any appropriatetype of image data 44. For example, the image data 44 can includepatient specific image data that can be acquired at any appropriatetime. The image data can include magnetic resonance imaging data (MRI)that can provide structural anatomical image data (i.e., such as a nasalcavity, etc.) of the patient 22. The image data 44 can be displayed onthe display 42 for use during a procedure by the user 50. The display 42can also include various atlas image data. Atlas image data can includetwo-dimensional image data sets, three-dimensional image data sets, andeven four-dimensional image data sets that show the change of variousanatomical structures over time.

With reference now to FIG. 2A, the electromagnetic tracking device 14 isshown operatively coupled with the exemplary handpiece 12. One suitablehandpiece is commercially available under the name “MENT M4Straightshot™ Handpiece”, sold by Medtronic, Inc. The handpiece 12 caninclude a removably (or non-removably) attached working member 80, suchas a debrider, bur or blade for example. The blade 80 can include ablade tip 82. According to the exemplary embodiment, the blade tip 82can be specifically adapted for ear, nose and throat (ENT) surgicalprocedures for burring or shaping various ENT cavities. While only oneblade 80 is shown, the EM image-guided surgery system 10 can include aplurality of blades each having different characteristics. The locationof a respective tip (i.e., 82) for each blade (i.e., 80) can beprogrammed into the image-guided surgery system 10, such as at aterminal connector of the handpiece 12.

In one example, the working member 80 can be part of a blade assembly84, FIG. 2B that is fixed to the electromagnetic tracking device 14. Inanother example, the working member 80 or the blade assembly 84 as awhole can be releasably coupled to the electromagnetic tracking device14. The blade assembly 84 can include an outer hub 86 having locatingtabs 88 and an aspirating port 90. A rotating hub 92 can be arrangedintermediate of an inner tapered hub 94 and the outer hub 86. In anassembled position (FIG. 2A), the locating tabs 88 can engage structure(not specifically shown) on the handpiece 12. During use, rotatablemotion is imparted into the rotating hub 92 for rotating within andrelative to the outer hub 86.

With reference now to FIG. 3A, an exploded view of the EM instrumenttracking device 14 is shown. The EM instrument tracking device 14 cangenerally include a body or housing 100 that comprises a base 102 and acap 104. The cap 104 defines a cap opening 106 at a distal end 108 and afirst and second lobe 110 and 112, respectively formed at a proximal end114. The cap 104 includes a cap body 116 that defines a generallyconical shape that tapers radially outwardly from the distal end 108 tothe proximal end 114. A cap extension portion 120 is formed on the cap104 generally between the first and second lobes 110 and 112. Anaccommodation portion 122 is formed generally on the conical section ofthe cap body 116 and aligned with the cap extension portion 120.

The base 102 generally includes a base opening 126 formed at a distalend 128. The base opening 126 can be concentric with a shaft of theworking member 80. A base longitudinal axis 129 can be defined throughthe base opening 126. The longitudinal axis 170 of the handpiece 12 canbe collinear with the base longitudinal axis 129 (FIG. 5). A secondtracking coil support 130 and a third tracking coil support 132 can beformed at a proximal end 134 of the base 102. The base 102 generallyprovides a base body 136 that is in the form of a conically taperedsection that expands radially outwardly from the distal end 128 of thebase 102 to the proximal end 134 of the base 102. A cable support 140 isformed on the base 102 generally between the second tracking coilsupport 130 and the third tracking coil support 132. A first trackingcoil 142 is generally disposed around the distal end 128 of the base 102proximate to the base opening 126. A second tracking coil 144 isdisposed generally within the second tracking coil support 130. A thirdtracking coil 146 is generally disposed within the third tracking coilsupport 132. The second and third tracking coils 144 and 146 aredisposed radially outwardly in the body 100 relative to the firsttracking coil 142. Explained differently, each of the second and thirdtracking coils 144 and 146 occupy a position offset radially relative toa circumference of the first tracking coil 142. Each of the first,second and third tracking coils 142, 144 and 146 are electricallyconnected to a terminal, such as a printed circuit board 148. A cableassembly 151 is electrically connected to the printed circuit board 148.In another example, a base 102′ can be provided (FIG. 3B) where theprinted circuit board 148 can be eliminated and the terminal ends ofeach tracking coil 142, 144 and 146 can each be electrically connectedto respective wires of the cable assembly 151. A longitudinal support150 can extend from the cable assembly 151 and be secured to the base102′. The longitudinal support 150 can provide additional strength tothe cable assembly 151 where it attaches to the base 102′ to inhibitinadvertent separation of the cable assembly 151 from the base 102′. Inone example, the longitudinal support 150 can be formed of Kevlar® andbe adhesively attached to the base 102′. Adhesive can also be disposedin grooves of the base 102′ at the respective connections between theterminal ends of the tracking coils 142, 144 and 146 and thecorresponding wires of the cable assembly 151. Again, as mentionedabove, the instrument tracking device 14 can communicate wirelessly tothe navigation handpiece assembly.

As can be appreciated, in an assembled position (i.e., FIG. 2, 4 or 5),the cap 104 is configured to be assembled generally over the base 102.In the assembled position, the distal end 108 of the cap 104 can enclosethe first tracking coil 142 disposed on the distal end 128 of the base.Similarly, the first lobe 110 of the cap 104 can enclose the secondtracking coil 144 and second tracking coil support 130. The second lobe112 of the cap 104 can enclose the third tracking coil 146 and thirdtracking coil support 132. The cap extension portion 120 can enclose thecable support 140. The accommodating portion 122 of the cap 104 canenclose the printed circuit board 148. In one example, a flowableadhesive, such as an epoxy can be disposed within the annular spacedefined between the base 102 and the cap 104 upon assembly formaintaining the cap 104 and base 102 in a secured position relative toeach other. In one example, the body can be formed of molded plastic.The second and third tracking coils 144 and 146 can be molded into thebase 102. Alternatively, the second and third tracking coils 144 and 146can be glued to the base 102. Epoxy can then be urged around the secondand third tracking coils 144 and 146 in the base 102 to retain thesecond and third tracking coils 144 and 146. The EM instrument trackingdevice is simple to manufacture and easy to manipulate onto and off ofan instrument 12.

With additional reference now to FIGS. 4-6, additional features of theEM instrument tracking device 14 will be described. The first trackingcoil 142 defines a first tracking coil plane 152. The second trackingcoil 144 defines a second tracking coil plane 154. The third trackingcoil 146 defines a third tracking coil plane 156. For purposes ofdiscussion, each of the tracking coil planes 152, 154 and 156 aredefined through a horizontal centerline of each of the respectivetracking coils 142, 144 and 146, respectively. As illustrated in FIGS. 4and 5, the first, second and third tracking coil planes 152, 154 and 156are all arranged orthogonally relative to each other. Additionally, eachof the first, second and third tracking coils 142, 144 and 146 define acenter point (i.e., the point at which their respective axes 162, 164and 166 intersect their respective tracking coil planes 152, 154 and156) that do not overlap.

A first tracking coil axis 162 is defined through the first trackingcoil 142. A second coil axis 164 is defined through the second trackingcoil 144. A third tracking coil axis 166 is defined through the thirdtracking coil 146. As best illustrated in FIG. 4, the second coil axis164 is perpendicular relative to the third coil axis 166. The firsttracking coil axis 162 is collinear with a longitudinal axis 170 definedby the handpiece 12. The first tracking coil 142 is therefore arrangedperpendicular relative to the longitudinal axis 170 of the handpiece 12and concentric with the working tool axis.

In use, each of the first, second and third tracking coils 142, 144 and146 sense the electromagnetic field produced by the coil arrays 64 and66 and generate an output signal to the navigation handpiece interface70 indicative of a position of the working member 80, and morespecifically the blade tip 82. The specific tracking coil configurationof the present disclosure where the first, second and third trackingcoils 142, 144 and 146 are positioned orthogonally relative to eachother and in the specific configuration relative to the shaver reduceselectromagnetic interference from the handpiece 12, which contains asubstantial amount of metallic material. The tracking coils 142, 144 and146 can provide positional, translational and rotational information (6degrees of freedom) along the respective axes 162, 164 and 166, alongthe respective planes 152, 154 and 156, and around the respective axes162, 164 and 166 for the instrument tracking device 14 as a whole.

As can be appreciated, by utilizing three tracking coils (142, 144 and146), the EM image-guided surgery system 10 can identify the locationand orientation of the set of coils 142, 144 and 146 in space andtherefore can calculate the location of the blade tip 82 in3-dimensional space. In this way, translational motion along the X, Yand Z axes as well as yaw, pitch and roll relative to the patient 22 canbe determined.

As discussed above, the EM instrument tracking device 14 may beremovably attached or fixed (non-removably attached) to the handpiece12. In one example, the EM instrument tracking device 14 can be slidablyadvanced over a distal end of the handpiece 12 and secured with aconnection mechanism 168. The connection mechanism 168 can compriseadhesive, cooperating threads, clips, snaps, fasteners or other device.Explained generally, the distal end of the handpiece 12 can be insertedthrough a passthrough defined by the base opening 126. In otherarrangements, the EM instrument tracking device 14 may be releasablycoupled to the handpiece 12, such as by way of a snap-fit connection. Itis contemplated however that the EM instrument tracking device 14 can beremovably affixed to the handpiece 12 by any suitable method. In generalhowever, the EM instrument tracking device 14 is disposable and becausethe EM instrument tracking device 14 is removably attached to thehandpiece 12, it can also be easily replaced.

The electromagnetic tracking device 14 is low profile and aestheticallypleasing to the user 50 when attached to the handpiece 12. Explainedfurther, the respective first and second lobes 110 and 112 thataccommodate the second and third tracking coils 144 and 146,respectively protrude radially outwardly a minimal distance. In oneexample, the base opening 126 can define a diameter 174. An outermostdistance 176 can be defined from the first coil axis 162 to an outermostdimension of the body 100 (i.e., at the first or second lobe 110 or112). The distance 176 is less than three times the diameter 174.Because the body 100 provides a low profile configuration, the user 50is afforded a greater viewing angle at the area of interest. In thisway, the body 100 is substantially free from obstructing a line of sightby the user 50 during the surgical procedure, such as down the sightline or axis of the instrument 12.

With reference to FIG. 7, the EM instrument tracking device 14 can beprovided with the cable assembly 151 and an electrical connector 180 atan opposite end. The EM instrument tracking device 14, the cableassembly 151 and electrical connector 180 can be contained in ahermetically sealed bag 182 prior to being attached to the blade 80.

In other examples, the EM instrument tracking device 14 can be providedwith fewer or additional tracking coils than the three tracking coils142, 144 and 146 described above. Moreover, the tracking coils 142, 144and 146 can be arranged at alternate locations on the body 100. In oneconfiguration as illustrated in FIG. 8, an EM instrument tracking device14′ can include a first tracking coil 142′ that is located around theperimeter of a base 102′ at a radially offset position relative to asecond and third tracking coils 144′ and 146′. In one example, the firsttracking coil 142′ can be located within a third lobe 113′ of a cap104′. The second and third tracking coils 144′ and 146′ can be locatedwithin a first and a second lobe 110′ and 112′, respectively. The first,second and third radially extending tracking coils 142′, 144′ and 146′can be supported by tracking coil supports 133′, 130′ and 132′,respectively. In the example illustrated, the first, second and thirdtracking coils 142′, 144′ and 146′ define tracking coil planes 157′,154′ and 156′ that are located at substantially 120° relative to eachother substantially perpendicular to the longitudinal axis 170. Otherconfigurations and/or radial offsets are contemplated.

The description of the present teachings is merely exemplary in natureand, thus, variations that do not depart from the gist of the presentteachings are intended to be within the scope of the present teachings.Such variations are not to be regarded as a departure from the spiritand scope of the present teachings.

What is claimed is:
 1. An instrument tracking device for an instrument,wherein the instrument has an elongated housing extending along a firstlongitudinal axis and includes a working member at a distal tip of theinstrument, the instrument tracking device comprising: a body that hasan opening along a second longitudinal axis of the body, wherein thebody is configured to be attached to the elongated housing such that atleast a portion of the working member extends through the opening, andwherein the first longitudinal axis and the second longitudinal axis arecollinear; a first tracking coil disposed in the body and radiallyoffset relative to the second longitudinal axis, wherein the firsttracking coil defines a first tracking coil plane, wherein the secondlongitudinal axis line intersects the first tracking coil plane suchthat the second longitudinal axis extends within the first tracking coilplane, wherein the first tracking coil generates a first output signalindicative of a position of the working member relative to the firsttracking coil plane; a second tracking coil disposed in the body andradially offset relative to the second longitudinal axis, wherein thesecond tracking coil defines a second tracking coil plane, wherein thesecond longitudinal axis line intersects the second tracking coil planesuch that the second longitudinal axis extends within the secondtracking coil plane, wherein the second tracking coil generates a secondoutput signal indicative of the position of the working member relativeto the second tracking coil plane; a third tracking coil disposed in thebody and radially offset relative to the second longitudinal axis,wherein the third tracking coil defines a third tracking coil plane,wherein the second longitudinal axis line intersects the third trackingcoil plane such that the second longitudinal axis extends within thethird tracking coil plane, wherein the third tracking coil generates athird output signal indicative of the position of the working memberrelative to the third tracking coil plane; and wherein the firsttracking coil, the second tracking coil and the third tracking coil arerespectively wound about a first tracking coil axis, a second trackingcoil axis and a third tracking coil axis, the first tracking coil, thesecond tracking coil and the third tracking coil are located at 120°positions relative to each other and about the second longitudinal axis,the first tracking coil axis, the second tracking coil axis, and thethird tracking coil axis are (i) orthogonal respectively to the firsttracking coil plane, the second tracking coil plane, and the thirdtracking coil plane, and (ii) in a plane orthogonal to the secondlongitudinal axis.
 2. The instrument tracking device of claim 1, whereinthe first tracking coil plane, the second tracking coil plane, and thethird tracking coil plane intersect each other at the secondlongitudinal axis.
 3. The instrument tracking device of claim 1, furthercomprising a connection mechanism configured to secure the body to theelongated housing, wherein at least a portion of the elongated housingextends through the opening of the body.
 4. The instrument trackingdevice of claim 3, wherein the connection mechanism is selected from agroup consisting of adhesive, cooperating threads, clips, snaps andfasteners.
 5. The instrument tracking device of claim 1, wherein thebody comprises: a base having the first tracking coil, the secondtracking coil and the third tracking coil disposed at least partiallywithin the base; and a cap that covers the base.
 6. The instrumenttracking device of claim 5, wherein the base and the cap are formed ofplastic.
 7. The instrument tracking device of claim 1, wherein: theinstrument comprises a surgical handpiece; and the working membercomprises one of a blade or a bur.
 8. The instrument tracking device ofclaim 1, wherein: the first tracking coil extends radially outward fromthe body; the second tracking coil extends radially outward from thebody; and the third tracking coil extends radially outward from thebody.
 9. The instrument tracking device of claim 1, wherein: the bodyincludes a cable support; and the cable support is configured to supporta cable assembly external to the body and between the first trackingcoil and the second tracking coil.
 10. The instrument tracking device ofclaim 9, further comprising a printed circuit board attached to thebody, wherein: the first tracking coil, the second tracking coil, andthe third tracking coil are electrically connected to the printedcircuit board; and the cable assembly is electrically connected to theprinted circuit board.
 11. The instrument tracking device of claim 10,wherein: the printed circuit board comprises terminals; the firsttracking coil comprises first wires; the second tracking coil comprisessecond wires; the third tracking coil comprises third wires; the cableassembly comprises fourth wires; and the first wires the second wiresand the third wires connect to the fourth wires at the terminals,respectively.
 12. The instrument tracking device of claim 11, whereinthe printed circuit board is mounted on the body distal of the firsttracking coil, the second tracking coil and the third tracking coil. 13.The instrument tracking device of claim 1, further comprising: a cableassembly mounted on the body; a longitudinal support member mounted onthe housing and comprising a plurality of grooves, wherein: the firsttracking coil comprises first wires; the second tracking coil comprisessecond wires; the third tracking coil comprises third wires; the cableassembly comprises fourth wires; and the first wires the second wiresand the third wires connect to the fourth wires within the grooves,respectively.
 14. An instrument comprising: the instrument trackingdevice of claim 1; a rotating hub connected to and proximal of theinstrument tracking device; and the working member, wherein the workingmember is connected to and rotated by the rotating hub.
 15. Theinstrument of claim 14, wherein the working member comprises a blade.16. An instrument tracking device of an instrument, wherein theinstrument has an elongated housing extending along a first longitudinalaxis and includes a working member at a distal tip of the instrument,the instrument tracking device comprising: a body extending along asecond longitudinal axis, wherein the body is configured to be attachedto the elongated housing of the instrument; a first tracking coildisposed on the body and radially offset relative to the secondlongitudinal axis, wherein the first tracking coil generates a firstoutput signal indicative of a position of the working member relative toa first tracking coil plane; a second tracking coil disposed on the bodyand radially offset relative to the second longitudinal axis, whereinthe second tracking coil generates a second output signal indicative ofthe position of the working member relative to a second tracking coilplane; a third tracking coil disposed on the body and radially offsetrelative to the second longitudinal axis, wherein the third trackingcoil generates a third output signal indicative of the position of theworking member relative to a third tracking coil plane; and wherein thefirst tracking coil, the second tracking coil, and the third trackingcoil are radially disposed at 120° positions relative to each otherabout the second longitudinal axis, a plane orthogonal to the secondlongitudinal axis intersects the first tracking coil, the secondtracking coil and the third tracking coil, a radius of the firsttracking coil extends in a direction parallel to the first tracking coilplane, a radius of the second tracking coil extends in a directionparallel to the second tracking coil plane, a radius of the thirdtracking coil extends in a direction parallel to the third tracking coilplane, and the first tracking coil plane, the second tracking coil planeand the third tracking coil plane intersect each other at the secondlongitudinal axis.
 17. The instrument tracking device of claim 16,wherein the body includes: a first lobe that projects radially from thebody and holds the first tracking coil; a second lobe that projectsradially from the body and holds the second tracking coil; and a thirdlobe that projects radially from the body and holds the third trackingcoil.
 18. The instrument tracking device of claim 16, further comprisinga longitudinal support member connected to the body and configured tohold a cable, wherein: terminal ends of each of the first tracking coil,the second tracking coil and the third tracking coil are electricallyconnected to wires of the cable; and the longitudinal support memberprevents separation of the cable from the body.
 19. An instrumentcomprising: an elongated housing extending along a first longitudinalaxis; a working member at a distal tip of the instrument; a body havinga base and a cap, wherein the cap covers the base, wherein the bodyextends along a second longitudinal axis and is attached to theelongated housing; a first tracking coil disposed on the body andradially offset relative to the second longitudinal axis, wherein aradius of the first tracking coil extends in a direction parallel to afirst tracking coil plane, and wherein the first tracking coil generatesa first output signal indicative of a position of the working memberrelative to the first tracking coil plane; a second tracking coildisposed on the body and radially offset relative to the secondlongitudinal axis, wherein a radius of the second tracking coil extendsin a direction parallel to a second tracking coil plane, and wherein thesecond tracking coil generates a second output signal indicative of theposition of the working member relative to the second tracking coilplane; and a third tracking coil disposed on the body and radiallyoffset relative to the second longitudinal axis, wherein a radius of thethird tracking coil extends in a direction parallel to a third trackingcoil plane, wherein the third tracking coil generates a third outputsignal indicative of the position of the working member relative to thethird tracking coil plane, wherein the first tracking coil, the secondtracking coil, and the third tracking coil are disposed at radiallyequidistant locations around the body, the first tracking coil plane,the second tracking coil plane, and the third tracking coil planeintersect each other, and a plane orthogonal to the second longitudinalaxis intersects the first tracking coil, the second tracking coil andthe third tracking coil.
 20. The instrument of claim 19, wherein: thebody has an opening along the second longitudinal axis; the body isconfigured to be attached to the elongated housing such that at least aportion of the elongated housing extends through the opening; and thefirst longitudinal axis and the second longitudinal axis are collinear.21. The instrument of claim 19, wherein: the body includes a cablesupport member; and the cable support member is configured to hold acable external to the body and between the first tracking coil and thesecond tracking coil.
 22. The instrument tracking device of claim 21,further comprising a printed circuit board attached to the body,wherein: the first tracking coil, the second tracking coil, and thethird tracking coil are electrically connected to the printed circuitboard; and the cable is electrically connected to the printed circuitboard.